Piezoelectric crystal plate



Oct. 18, 1949.

H. G. BAERWALD PIEZOELECTRIC CRYSTAL PLATE Original Filed March 19, 1945 ALL THREE PLATES X EQUIVALENT wemp FIG. 2

INVENTOR. HANS G. -B,AERWALD A TOR NEY Patented Oct. 18, 1949 PIEZOELECTRIC CRYSTAL PLATE Hans G. Baerwald, Cleveland Heights, Ohio, al-

signor to The Brush Development Company, Cleveland, Ohio, a corporation of Ohio Original application March 19, 1945, Serial No. 583,477. Divided and this application April 10, 1948, sci-m No. 20,174

This application is a division of my application Serial Number 583,477, filed March 19, 1945, for Piezoelectric crystal plates, to which reference may be made for a complete discussion of the invention with respect to all crystal classes to which the invention is applicable.

This invention relates to cuts of piezoelectric crystals and more particularly to thickness-controlled shear crystal plates for frequency control or as filter elements in the upper radio and ultrahigh frequency range.

The fundamental object of this invention is to provide from crystal classes Iiv and In, and the cuts or orientations therein possible by virtue 01' the laws of phenomenological crystal physics, plates with the following three fundamental properties:

1. They are excitable in simple-mode thicknesscontrolled elastic shear vibrations by longitudinal electric fields and/or dielectric displacements;

2. No elastic and dielectric interaction of these shear modes with any other modes of vibration exists;

3. These orientations are independent of the physical constants of any particular material belonging to one of the specified classes of crystallographic symmetry as Well as of extraneous physical conditions such as temperature.

For the purpose of this description. cuts with these three roperties are called piezoelectric unconditionally pure thickness-controlled shear cuts.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In accordance with a feature of the invention there is provided a piezoelectric thickness-controlled shear crystal plate cut from crystalline piezoelectric material having a crystallographic plane of symmetry containing an inversion-rotation axis. The plate which is cut from the above described crystalline material has a pair of plane parallel major faces which are substantially parallel to a crystallographic plane of symmetry.

With respect to the drawings. Fig. 1 shows the orientation of piezoelectrically active crystal plates having thickness-controlled uncondition- 3 Claims. (Cl. 171-827) ally pure shear modes of vibration for a material of the class I4v=(Va) and Fig. 2 illustrates the corresponding conditions for the class In.

From the arguments advanced in the description in the parent application it follows that of all unconditionally pure shear waves possible under the crystallographic symmetry of classes I4v and 16v, only one is piezoelectrically excitable by longitudinal fields. These fields are perpendicular to the many of the equivalent crystallographic planes of symmetry and the direction of motion associated with the shear vibration is parallel to the Z axis in case of 14v and parallel to a Y axis in case of Idv, the X axis in the latter case being defined by the usual convention as being perpendicular to the mirror plane. Therefore, in both classes, the desired plates lie parallel to the crystallographic planes of symmetry, of which there are two equivalent ones in class Iiv and three in class Isv.

These are all of the piezoelectric classes having a crystallographic plane of symmetry containing an inversion-rotation axis of an order higher than two.

As in the angular neighborhoodof any pure shear cut undesired elastic interactions are proportion to the square of an angular deviation only and, therefore, are practically eliminated throughout that neighborhood, moderate angular deviations cannot only be tolerated but may even be desirable if they lead to a slight improvement in the temperature coeiilcients.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention. and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a piezoelectric thickness-controlled shear crystal plate: a plate cut from crystalline piezoelectric material having a crystallographic plane of symmetry containing an inversion-rotation axis, said plate having a pair of plane parallel major faces which are substantially parallel to said crystallographic plane of symmetry.

2. In a piezoelectric thickness-controlled shear enu 3 4 ,cmtelpletezeplntecutimcryetdllneplmelectric material oftheclmlmaeldplete humm m lnzepeirotplenepuallelmadorhceewhlchm iml' mmdmhtbe subetentiellyparallelteea'yetelloznphicplme meolfllllmti of symmetry of said meterlal. 5 m

3. In a piezoelectric thickness-controlled cheer m crystal plate: a platecut from crystalline plelo- W ID. nu. electric material of the class In, said plate having 3 M Dec. 1, 1942 e peir oi plane parallel meJor feces which are 3 Mueller Dec. 20, 1942 substantially parallel to a. crystallomphlc plane 10 mm 3 0! symmetry of said material. on

cm. w. a. Pleloeleetrleity, llcGrew-Hlll, ms 0. BAERWALD. m 1 pm I0. 

